Sharing..

So that day has come...the day that Jillian wants all the toys that Madelyn is holding and the subject of sharing is upon us...With two little girls two week or so shy of 18 months apart we new it was inevitable. So the question that I pose now is this- when teaching children to share what is right? I know that I can't let Jillian have anything of Madelyn's that she wants that she has to learn that some of Mad's toys are just her's--such as her two beloved "blankies". What I need advice on is what the fine line is-- I know that Madelyn needs to learn to share but Jillian also needs to learn that just because she is the little sister she can't have any toy that she wants. Thoughts or comments anyone? Or am I perhaps over thinking the whole situation and just go with my gut? and of course I will end with a picture of my lovies...